The present invention relates to a braking pressure control device, in particular an anti-lock control device (ABS-device), and a traction slip control device (ASR-device), for automotive vehicles. The device comprises a master cylinder, wheel cylinders, at least one pump for positioning at least one piston of the master cylinder, a pressure modulator modulating the pressure in the wheel cylinders during the control mode, and an electronic control unit processing the wheel sensor signals to corrective signals for the opening valves and shut-off valves of the pressure modulator. The device further comprising a brake power booster, in particular a vacuum brake power booster which comprises a housing, a piston element, in particular a diaphragm plate, and a diaphragm, such as a rolling diaphragm, which interconnects the piston element and the housing in a sealing manner, and which permits movements of the piston element in relation to the housing, with the piston element being in operative engagement with the brake pedal.
Anti-lock systems are used in the motor vehicle industry in increasingly large numbers. In certain specific applications of these anti-lock systems, hydraulic pumps are used for generating an auxiliary pressure during the control mode. Such an anti-lock device has been described, for example, in German patent application P 3731603.6, corresponding to U.S. Pat. No. 4,826,255.
U.S. Pat. No. 4,826,255 discloses a brake system, in particular for automotive vehicles, comprising a master cylinder, wheel cylinders and a device for anti-lock control. In this brake system, there is provided a pressure-fluid source, in particular a pump, for positioning the piston of the master cylinder in a desired position during the anti-lock control mode. The rate of delivery of the pump is variable, and communicated by way of a hydraulic line with the master cylinder to be able to position the piston in accordance with its rate of delivery.
The present invention has the following objects: It is particularly desired that the brake pedal be positioned forward of an initial, fully retracted position in a particularly simple way during the anti-lock or traction slip control mode. The position of the push rod piston of the master cylinder sets the desired position of the brake pedal forward of its initial position. The further objects of the present invention are to provide an arrangement providing for the stroke of the push rod piston to be defined by a switch which does not enlarge the overall length of the entire assembly, composed of a vacuum brake power booster and master cylinder.